Being able to shut down reactors should stay. But instead of the on/off switch like its a light bulb it should be a sudden stop, where it destroys the cells in the reactor.
As for it being more realistic and dynamic: The uranium cells could lose the power they output with time, changing their heat levels, so if you want more power, you would have to overprovision during start so you have more power in later stages of the cycle.
Also a neutron shield item that goes between the UC that controlls how much neutrons pass between cells.
Say like this:
Uranium sends neutrons to every other cell in line, not just adjacent, every one. Depending on distance it changes the amount it amplifies. Neutron shield goes inbetween stopping some/all of the neutrons.
There should be a output pipe/item that absorbs heat and turns it into power, so you would need to get that power to the output, not just stay in the reactor. So more heat in said pipe=more power. What this means is, uranium is used to make heat, it does not create power by itself, power comes from OUT-PIPE. Again it would be in your interest to keep the heat high.